baden



J. Jo'NAs ET AL MERCURY VAPOR PUMP FOR HIGH VACUUMS July 11, 1923-dii/ys.

2 Sheets-Sheet 1 Filed June 6. 1921 July 17, 1923 1,462,112

J. JONAS ET AL MERCURY VAPOR PUMP FOR HIGH VACUUMS Filed June 6, 1921 2Shoots-Shut 2 i Application led June 6,

Pahen'ted July 17, 1923.

UNITED STATES PATENT OFFICE.

JULIUS JONAS, OF MEIERHOF, BADEN, AND OSKAR SEITZ, OF OBEEERKAPEELERHOF, BADEN, SWITZERLAND, ASSIGNORS `TO AKTIENGESELLSCHAFTBROWN'BOVERI 8;

CIE., OF BADEN, SWITZERLAND.

1T 0 all whom t may concern Be it known that we, JULIUs JONAS, a citizenof the German lRealm, residing at Meierhot, Baden, Switzerland, andOsKAR Snrrz, a citizen of the Swiss Republic', residing at ObererKappelerhof, Baden, Switzerland, have invented certain new and usefulImprovements in Mercury-/vapor lPumps for High Vacuums, of which the':following is "ai specication.

Various constructional forms of'mercury vapor pumps havey been proposedfor producing high vacuums. Those pumps consist of a closed rvvesselcontaining mercury, provided with a pipe for connection to the'preliminary vacuum pipe.` and a pipe for coinnection with the receiver,and in which, on the yone hand, the mercury is vaporized by a heatlingdevice, and onthe other hand the mercury vapor is condensed by aycooling device. n y

ln operation, the lowingmercury vapo-r :mingles with. the air issuingfrom` the receiver and bindsfit, and on `condensing,.gives it up againat that partof the vessel where the connection with the preliminaryvacuum pump issituated.

The existing constructlonal forms of this y kind of pump are more orless complicated, because the interior of the pumphas contained hithertoguide partitions and covering plates .and also cylindrical insertions,for the purpose of effecting the desired er:-` traction by suction ofthe very smallest traces of air from the receiver. The idea that thekinetic energy of the iiowing mercury vapor plays an essential part. invsucking the air from the receiver, forms the basis of the presentinventioinwhich provides an air pump, the construction ot whichisextremely simplified compared with the known constructions. n i

The improved pump is'based on the4 idea of utilizing yas vcompletely aspossible the kinetic energyv of the mercury vapor and guiding themercury vapor in such a ,manner that itv will reachthe workingpointbythe shortest way and in the `proper condition of vapor. AFurther,in the improved form of the pump body resulting vfrom this feature,`

the airsupply place vis so constructed and arranged that no ymercuryvapor is able to flow into .the air supply pipe, thereby 0bviating thecounteraction ofall vagrant mercury vapors. y

MERCRY-VAPOR yIPUIVIP FOR HIGH VACUUMS 192,1.y serial No. 475,486.

densed'mercury particles has considerable advantages as regards theworking of the pump, and that it is distinctly disadvanta? geous to havea separa-te guidance such as is provided in the pumps hitherto known.

The use of the same chamber is not only a considerable simplilication asregards the construction of the pump, but it also allows a betterutilization of the supply energy both for increasing the volumetricoutput, as well as for increasing the pressure drop, in which, asalready stated, the streamof vapor flows without being throttled, by theshortest and straightest possible path to the working point. The workingchamber proper of the pump is thus divided into the mixing space and thecondensing space, these spaces however are not divided sharply from oneanother but merge into one another.

The present invention hasr therefore for its object to provide a mercuryvapor pump l'or producing high vacuums consisting of a mercury isvaporized by a heating device, n

and on the other hand the mercury vapor is condensed by a coolingdevice, the arrangement being such that the flowing mercury vapormingles with the air issuing from the receiver and binds it, but givesit up again on condensing at that part of the vessel where theconnertion of the preliminary vacuum pump is located. f

Above the heating chamber there is provided for guiding the ascendingvaporized mercury as well as the falling mercury drops, an internallyunobstructed tube at the upper end of'which the connection to thepreliminary vacuum pump is located whilst the air to be drawn oil' isted to the lowerend of this tube, and a cooling device is providedbetween these.twonconnecting points. p

The construction of an improved pump according to this invention isillustrated diagrammatically in Fig. l of the accompanying drawings.

As shown, the main portion of the pumppoint on entry.

is situated by the vertical lvessel a, the lower and somewhat enlargedpart of which contains a quantity of mercury IL. This mercuryisheated bya Bunsen burner t'. The mercury vapor flows upward through -the tubularcylindrical part 7c of the vessel a, where it condenses on the cooledpart m of the said vessel. Forthis latterpurpose the part m issurrounded by a jacket CZ to which the cooling liquid gissupplied at eand passes out therefrom at The upper end of the vessel @terminates inja tubular extension c to-whichthe `preliminary vacuum pump is connectedat 0.

Below the cooling jacket d a'pipe opens into the vessel a at right.angles to the axis of the said vessel, approxin'iately at `the pointwhere the `mercury vapor assumes the form of mist,`this point havingbeen found in practice to `be the most `favourable The air which issucked out of the receiver at 7L is thus caused at Z toimpingeapproximately at right angles against the stream of mercury vaporand is carried along by the latter.

After the mixture has traversed the cooling' zone this air is releasedand is then sucked out atc by the.preliminary vacuum pump. Instead ofvthe Bunsen burner any other sort of heat, for instance electricity, maybe employed.

In this improved pump in which it is of importance to cause the mercuryvapor to pass with great velocity by the shortest path to the workingpoint, that is to say into the condensing chamber 0f the pump, theintended purpose is effected ina high degree constructing the air supplypoint in the manner shown in the ligure. r

The entire construction of the pump differs from what has been knownhitherto also in this that in the improved pump the mercury vapor,instead of flowing from a narrow tube into a wide tube, flows on thecontrary from a wide tube (the heating` chamber) into a narrower tube(the mixing` chamber and condensing chamber).

The density of the vapor thus becomes great and consequently theattainable pressuredrop of the pump also increases. By the expressionpressure-drop there is meant the pressure-difference between thepreliminary vacuum pressure at which the high vacuum pump will j ustwork fully, and the high vacuum attainable therewith.

This increase in the density of the vapor is permissible in this casebecause the pump tube isfree from internal obstruction and therefore thevapor pressure can be converted without hindrance into motion. ln thismotion, however, the vaporized condition does not remain the same.l/Vhereas in the heating' chamber the vapor is superheated, that is tosay is dried, it is intended that in the mixing chamber it shall alreadyresume the state of2mist, and in the' condensing` chamber shall becooled downto the point where the formation of drops begins.

It has been. found-.thatthemostavourrable mixing` lchamber consistsonlyofa rela-I tively small-.Zone Vin which'` the interrnin'gling` ofthe mercury vapor and air is to take place. Outside this -Zone thevaporized condition of the mercury is less suitable for takfing up theair because it is either still superthe stream of mercuryvapor doesnot-come into question. An inflow oflthe airparallel to the streamOfmerCury'prolongsthemixing` chamber because owing'to 'the vvparallelmovement ofthe vapor and of theair theinertia Voft'he'partsvret-ardstthe mixing process.

The'most favourable wayis theinflow of air at right angles, because thisproduces a rapid interpenetration of the twosubstances and the mixing?,`chamber is extended .only for a short vlengt-h in 'the direction o'f'thevInovement ofthe vapor.

The objectof the apparatus to cause the kinetic energy ofthe mercuryvapor to come into complete operation, and t0 convey the vapor'intothecondensing chamber with the least possible friction and lby theshortest path, is thus considerably facilitated by admission of air atright angles,

VSince the cooling device is situated outside the improved pump of thisinventiont a natural cooling `action (in the atmosphere) may be madesufficient to producea goed o'peration of the pump, especially when thepump is made of metal. This will depend upon `the shape of the coolingsurface, that is to say also upon the length of the .pump tube.

If the pump tube is made of a length suflicient for effective coolingthen, as already mentioned hereinbefore, the admission of the air musttaire place at that point of the tube where the gaseous mercury vaporbegins to assume the condition of mist. This arrangement is extremelysuitable for the construction of a multistage or pump for producing ahigh vacuum with a great pressure-drop because it affords, in additionto simplicity in assembling'the parts together. the further advantagethat all the parts are suitable to the very last detail. l

F or effecting` multistage working according to this invention aplurality, equal to the number of stages, of internally unobstructedtubes of different diameters for guiding the fici-ving` mercury vapor.are arranged conccntrically above the heating',- chamber in llU such amanner that theyare all traversed ing mercury vapor in the spaceybetween the 1 two outermost tubes, in which space yit is.

driven to the top where this annular space is closed to the outside, andvadmission aper#k t-ures for the'air that is released onthe condensationof the mercury, are provided in the inner adjacent annular space inwhich the rising mercury vapor' bindsagain the released air, and leadsit to the upperend of said space wherethe air, becoming again released,is led inthe same manner into the third annular space,v 'and so forth,`until the air which has been compressed severaltimes by this means inthe innermost tube is conveyed by the risingmercury vvaporto the tubularneck (located at the upper end ofV said tube) on its way tothepreliminary vacuum pump; the parts of all the tubes serving to guide thegaseous mixture beine; cooled by a cooling device thatis common to all.v

This pump will nowv be described more fully with reference tothefconstrurtional example illustrated in Fig. 1 e

In this gure i is the heatingfbody; it is the mercury contained in theheating chamber; as, afl, a2, (LR are the concentric guide tubes placedone into another fortheascending mercury vapor.r 'The length of the tubeL3- is greater than that of the tube as whilst the latter length isgreater than the length of the tube el which last`r nally, is 'greaterthan the length of the tube a The annular spaces comprised between thesetubes are closed at their other ends fromithe outside by caps anaal, m2,At these points,

however, in each `case there arefprovided apertures 0, 01, 02, o?, whichallow the air to enter the next inner annular spacer.,

The outermost tube t is provided with ka pipe neck b which is set atright angles toa and is connected with the receiver.

Thus the air l from theV receiver "flows through the aperture n! intothepipe neck e and from the latter into the annular space which isbounded by thev tube yandthe tnlnk mercury vapor becomes condensed onthesides of the tube lr, but only thecompressed airvpasses throughtheaperti y s o to the next inner annular space enclosed between kpointof admission of the air.

, purpose.y

the tubes ai ,and a2. Since mercury vapor is ascending also in thislatter space, the operation will be repeated in the same manner as oftenas there are steps in the pump.

The Lcompressed air ascending in the innermost tube a3 passes nally intothe pipe through which the multistage lcompressed air Venters the pipeleading to the preliminary vacuum pump.

is tobe noted that the mercury condensedin the several spaces runs downfreely back into the heated mercury vessel so that 1t is always the samesubstance that circulates between vaporization and condensation.

This improved pump ,constitutes` an interesting series arrangement ofv aplurality of pumps hereinbefore described,` in which ally the`pumps'combined in this manner have a common heating device, a commonheating` chamber, a common body of kmercury and a common cooling device,and it is an extremely favourable. feature that the i cooling waterwhich flows in through the pipe neck e and out through the pipe neck ,ffirst flows round the tube a into which the air enters'from thereceiver. The pipe neck l; is cooled as well and this is avery importantfeature because first it preventsl the entry of mercury vapor into thereceiver, and second the zone `in which the mercury vapor assumes theform of mist is thereby located exactly at the Since the pressure-dropis considerably increased. in the manner above-described by meansy ofthe multistage air pump, a considerably smaller preliminary vacuum pumpymay be employed, and in some cases even very simple jet pumps will befound suflicient. In the present case 1t is particularly advantageous toemploy 4as a preliminary vacuum pump a rneck cfwhoseupper end has anopening o3 l ion water jet pump which is fed with they cooli ing waterlof the high vacuum pump discharging through the pipe neck f, so thatthe waterthat is, used is made to serve a double An especiallyadvantageous construction of the improved pump is provided by a conicalformation of the internally unobstructed tube,` the connection to thepreliminary vacuum pump being made at the apex of the cone." The conicalpump bodyl thus stands-with a wide aperture upon the heating` chamberand tapers in the upward direction. The connecting pipe for the air tobe` sucked away is inserted from the side into the lower and widerportion of the mantle of the cone, The advantage of this arrangement isthat, owing to the taperingr ofthe tube, the yeffectiveness of thecooling increases in the upward direction so that ,In 'this manner thep'umplchamber is prevented trom becoming impoverished in mercury so thatthe pump can be Worked with a comparatively small quantity or mercury.

rlhe use et a small quantity of mercury also prevents the drawbacks of aretarded ebullition and thus a high4 elliciency is attained.

The improved pump is illustrated diagrannnatieally in section in Fig. 3Where in H is the heating chamberot the pump;

Q is the mercury;

F is the heating device;

P is the vconical pump chamber;

B is the admission pipe :tor the air flovving into the pump;

R is the point of connection to receiver;

k*O is the inlet aperture into the pump chamber for the air coming tromthe re-v ceiver;

V is the outlet aperture tromthe pump chamber for the air sucked by thevacuum pump;

V17 is the cooling liquid; and

K is theV cooling vemel withr the inlet Z and the outlet for the coolingmedium.

As shown in the figure5 the conical pump body tapers towards the airoutlet so that the cooling acts veryr energetically at the end or thecondensing operation.

This arrangement prevents entirely any mercury Jirom passing out of thepump chamber. vantage that the pipe B is also surrounded by the coolingliquid.

For the vpurpose of getting` a comparaL tively small mining chamber formining the sucked-in air withthe mercury that passes over in the form otmist, it is, as already stated, an advantage to lead the air to the pumptube in a direction at right angles to the direction of movement of themercury vapor. The ei'liciency of the pump is increased by the intensiveinterpenetrat-ion of the tivo substances in a comparatively small space,This circumstance 'also allows of reducing the total height or the pumpand ot rendering its construction moreeconomical.

The air coming from the receiver requires; however, a. Wide leading-inpipe in order to get a large volumetric eiliciency or output. Ii"- atube of circular cross-section is emplcyed the leading-in tube. then inthat case Awhen theintlow ot the air is at right angles, there vvill bea circular inlet into the pump chamber.r the cross-section ot whichinlet is equal to the cross-section of the Wide leadingein pipe. Thisshape of large inlet dimishes very considerably `the eiiicienc'y of thepump, On the one hand a considerable quantity of mercury vapor which isstill expanding notwithstanding its high velocity, enters the leading-inpipe and thereby counteracts in a considerable degree the effectivenessof the pump. On the other In this modification it is an ad;`

hand the mixing chamber necessitated by this relatively high inlet, isso great that the condition of the mercury vapor is not in all parts ofthe mixing chamber the very best or carrying with itthe maximum quantityor' air, so that the efficiency must be smaller on this groimd also.

According to this invention the air. admission pipe has still arelatively large circular cross-sectional area,y but just before itopens into the pump, Whilst retaining or having its cross-sectionincreased, it assumes a shape such that the inlet will have a smallerextent in the direction of the movement oit the mercury vapor than in adirec tion at right angles thereto... By this mea-ns; lirst the entr-yof the mercury vapor into the air admission pipe is prevented in apractically' sutlicient degree, and second the mixing chamber is reducedto a smaller size which is of advantage for the Operation and the' sizeof the pump.

A. constructional example of this modiication of the improved mercuryvapor vacuum pump is illustrated in Figure 4; in Whichry H is theheating chamber of the pump;

C). is the mercury; l

F is the heating device which may also be of electric nature;

l? is the pump chamber;

V is the pipe for connection to the preliminary vacuum pump;

is the pipe for connection With the receiver;

B is the admission pipe of circular crosssection for the air to besucked away by the pump; y

C is portion of the pipe B just before it opens into the pump;

O is the inlet for the air.

As shown in this ligure, the entry of the air into the pump chambertakes place in a direction at right angles to the direction or themovement or the mercury vapor. Inlet O is or rectangular shape with.according to this invention; the short side of the rectangle having thesame direction the :lirection of movement ot the mercury vapor. y y

The cross-section of the pipe changes from the circular shape into therectangular shape in the direction C of the pipe. K is the coolingvessel which surrounds both the upper part of the pump and the pipe B. Wis the cooling liquid which enters at the point Z into the coolingvessel K and passes out from the same vessel at the point A..

rIhe constructional example shown in this Fig. l has further importantadvantages.

In the tirst place it is to be noted that the end C ot the pipe which isat right an# gles to the direction of movement Yof the mercury vapor, isa certain length which is indispensibe for the proper working of thepfump. rPhe end C of the pipe must be of such length that no expandingmercury vapor particle can enter the pipe B without first having struckagainst ythe upper wall of the end C of thek pipe..`r By this 'striking'the kinetic energy oi!` the particle kis reduced to such an extent thatthejcu'rrent of air' passing through the pipe kB is not obstructed inany way by a counteracting flow of mercury vapor. f

. A 'urther advantage is to be found inV the `Ues'hape formed by `theair admission pipe B and the pump tube P, so that thel pipe and the pumphave actually the form of two communicating pipes. y -r y F orthereasons already stated, it is possible only k'withthek revision oit asuticiently long lengthl ,l to carry the pipe B vertically downwards. Inother respects they requisite length is kept comparatively small byconstructing the inlet O `in `the manner described. f

The illustratedU-shaped arrangement allows on the one hand the use of acommon cooling vessel for the air admission pipe and pumpinto which theentire apparatus is immersed, and on the other hand a convenientconnection to the receiver and to the preliminary vacuum` pump, nbecause 'both connections can be located side by side in the top orcover of the cooling vessel.

The cooling device is intended, Aas al-f ready stated, to cool the pumptube between the inlet and outlet for the air. The flat shape of theinlet O and oi' the end C of the pipe entails the risk that, yespeciallyin the case of a pump made of metal, the

cooling will act too tar downwards, that to say, actually upon theheating chamber.

that it will act upon the pump tube and f This premature cooling of theascending mercury vapor is injurious and reducesy the effectiveness ofthe pump. A 't In the improved construction therefore. the coolingdevice is made of such a size the air admission pipe in such a kmannerthat the gaseousmercury vapor will assume is provided as a guidefory theascending vaporized mercury and also for the fallingv drops ot condensedmercury, an internally unobstructed ltube at the upper end 'o'l" whichis located the connection tothe preliminary vacuum pump, whilst theconnection to the receiver is made at the lower end ot said tube; thecooling device' being klocated between thesev two. points of connection.m

2. A merucry vapor vacuum pump as claimed in claim l., characterized bythe featurethat the pipe conducting the air from the receiver to thepump enters the pump n in a direction `at 4right angles to the direc"`tion of the flow ofthe mercury vapor.

S. A; mercury vapor vacuum pumpV as claimed in claim l or -claim 2,characterized by the feature that the cooling device is the wall'oiZ theinternally unobstructed tube located above the heating chamber and thepipe leading the air out ci' the receiver enters the said tulbe at thatypoint koil'said tube where the gaseous mercury vapor begins-to `assumethe form of mist.

4. A mercury vapor vacuum pipe as claimed in claim l, including aplurality of'internally unobstructed tubes of different diametersserving toV guide theiiowing mercury vapor, the said -tubes being`arranged concentrically abovey a common heat- *ing chamber in such amanner that they are all traversed in the same axial direction by themercury `vapor generated in the said common ,heating chamber; thelengths ot said ltubes diminishing with their respec-k tive diameters,the lower part of the outermost tube being connectedto the receiver by atubularneck inserted approximately atvright angles, the annular spacebetween the adjacent tubes being closed at its upper end, except for anaperture in said upper end connecting each annular space to the nexttowards the axis, the preliminary vacu um pump connection being locatedat the upper end of the innermost tube; the partsy of all the tubesserving to guide the gaseous mixture being cooled 'by Aacooling devicethat is common to all said parts.

5. A mercury vapor vacuum pump as claimed in claim 4, characterized bythe feature that the preliminary vacuum pump, consists of a water jetpump' which is operated by the water that serves to cool the high vacuumpipe.

`6.* A mercury vapor vacuumL pump as claimed in claim 1, characterizedby the eature that the internally unobstructed pump tube located abovethe heating chamber is made conical and is seated with its wide end uponthe heating chamber, the connection to the preliminary vacuum pumpvbeing located at the apex ot the cone, and the connection withv thereceiver being located laterally and above the heating cham-` ber. n

7. A mercury vapor vacuum pump as izo claimed in claim 6, characterizedby the feature that both the conical surface orp the pump tube and theadmission pipe for the air coming from the receiver are cooled.

8. A mercury vapor vacuum pump as elaimedin claim 7, characterized bythe feature that the pump itseltl and the admission pipe for the aircoming from the receiver are both cooled in a common cooling vessel.

9. A mercury vapor vacuum pump as claimed. `in claim l, characterized bythe iieature that the pipe conducting theair lfrom the receiver to thepump is constituted by a tube of relatively large, preferably circularcross section, Which shortly before its aperture into the pump, assumesa shape of equal or increased cross section such that its said apertureis of less extent in the direction oit the movement oi the mercury vaporthan in a direction at right angles thereto.

10. A mercury vapor vacuum pump as claimed in claim 9, characterized bythe feature that the air admission pipe for the air to be sucked away,forms With the pump tube a U-shapcd device; the modiiied end of the airadmission pipe being` arranged at right angles to the direction of themovement of the mercury vapor and being made of a length such that noexpanding mercury yapor particle is able to enter the descending portionof said air admission pipe Without i'irst having struck against theupper Wall ot said end of said air admission pipe.

lla A mercury vapor vacuum pump as claimed in claim l, characterized bythe feature that the cooling device is so constructed that it acts uponthe pump tube and the point of admission or' the air in such a mannerthat the gaseous mercury vapor does not assume the form vof mist untilafter it has arrived above the heating chamber. ln testimony WhereoiC Wehave signed our naines to this specification.

' 'JULIUS JONAS.

ossee. SEIT@

